The present invention relates to devices for electrostatic spraying; more particularly, the invention relates to a system for monitoring voltage and current parameters of an electrostatic spraying gun or device, and for transmitting the monitored values to a remote location under nonhazardous conditions.
In the field of electrostatic spraying, and particularly electrostatic spraying of liquids having volatile components such as paint materials, there is a need to provide a safe operating environment for the spraying equipment. The principle of electrostatic spraying necessarily involves the use of a high voltage in a volatile environment, wherein it is desired to maintain a close control over operating current in order to avoid a combination of circumstances wherein ignition of the solvent vapors in the environment is possible. Therefore, a careful monitoring of the voltage and current operating conditions is necessary, and when the combination of current and voltage exceeds predetermined values the electrostatic system must be either shut down or reduced to safe operating conditions. A number of safety devices have been developed in the prior art in order to address this problem, some of which are summarized in the following paragraphs.
Since electrostatic spray devices always operate in a paint spray booth environment, in a volatile vapor environment, care must be taken to shield or isolate any electrical circuits associated with the equipment. It is desirable to wholly isolate the electrical equipment outside the spray booth from any electrical connection to the equipment operating within the spray booth. In the case of the electrostatic spray gun, the development of the air-powered electrical generating system described in U.S. Pat. No. 4,290,091, issued Sep. 15, 1981, and U.S. Pat. No. 4,219,865, issued Aug. 26, 1980, has permitted the electrical generation equipment for electrostatic voltages to be wholly confined within the spray booth, without exterior voltage connections. The present invention maintains this electrical isolation with respect to the voltage and current monitoring equipment associated with the spray gun. Therefore, the present invention enables an electrostatic spraying system to be operated within a paint spray booth, and the voltage and current operating conditions to be monitored outside the paint spray booth, in complete electrical isolation, so that no electrical conductors pass through the barriers between the paint spray booth and the outside environment.
Reference should be made to co-pending U.S. Pat. application Ser. No. 478,276 and Ser. No. 478,277, filed Feb. 9, 1990, for a disclosure of circuits within the spray apparatus of the aforementioned type, wherein the electrostatic voltage developed within the spray applicator may be monitored and converted into a variable frequency signal, and wherein the electrostatic current developed within the aforementioned apparatus may be converted into a variable frequency signal. The circuits described in the foregoing co-pending applications are utilized in conjunction with the present invention, to provide the necessary variable frequency signals representative of voltage and current which the present invention utilizes. The respective disclosures of the co-pending applications are incorporated by reference herein.